W. Pfleging1,4
1
Institute for Applied Materials – Applied Materials Physics, Karlsruhe Institute of
2
Institute of Functional Interfaces, Karlsruhe Institute of Technology,
3
4
Institute of Nanotechnology, Karlsruhe Institute of Technology,
5
89069 Ulm, Germany
Lithium-ion pouch cells consist of stacked layers of tape-casted
composite electrodes and separators. The electrodes exhibit typical film
thicknesses in the range of 50 – 100 µm. Nevertheless, thick composite
films suffer from insufficient wetting behaviour with liquid electrolyte
due to an increase in electrolyte penetration depth and therefore, poor
cycling performance at high charging and discharging currents. These
drawbacks can be overcome by recently developed laser process
strategies.
Laser structuring of selected composite electrode materials was performed
using Q-switched ytterbium-doped fiber laser radiation with a wavelength
of 1064 nm and pulse duration of 200 ns. The thermal impact of the laser
ablation process into the positive active material was investigated using
X-ray diffraction analysis as well as focused ion beam sample preparation
technique for cross sectional analysis of melted surface layers.
Furthermore, the heat impact zone was estimated by a numerical
calculation and the results were in good agreement with those obtained
from experimental studies.
It could be shown that vaporization of the binder matrix within the laser
interaction zone maintains the ablation process and therefore, the removal
of the composite electrode material down to the current collector. The
application of laser structuring technique enabled the formation of
capillary structures directly into the composite electrode accompanied by
rapid and efficient electrolyte wetting. Furthermore, it was shown that
lithium-ion cells composed of laser structured electrodes revealed
significantly improved reliability and capacity retention at high charging
and discharging currents for several thousands of cycles.